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Polarised Photon Beams for the BGO-OD Experiment at ELSA
Book title (Conference Proceedings)
Proceedings of the 10th International Workshop on the Physics of Excited Nucleons (NSTAR2015)
Volume
10
Place of Conference
Osaka, Japan
Year of Conference
2015
Publisher
The Physical Society of Japan
Pages
032003
ISSN/ISBN
978-4-89027-114-6
Abstract
The new BGO-OD experiment at the electron accelerator ELSA, of the University of Bonn, is designed to study the reaction dynamics of nucleon excitations in meson photoproduction. It consists of a central BGO calorimeter with a magnetic spectrometer in forward direction. The physics programme includes the measurement of polarisation observables using linearly and circularly polarised photon beams. Linear polarisation is obtained by coherent bremsstrahlung off a diamond crystal, and circular polarisation is obtained via bremsstrahlung from longitudinally polarised electrons. The degree of linear polarisation is determined from the bremsstrahlung spectrum itself. To determine the polarisation of the circularly polarised photon beam, the polarisation of the electron beam is measured by a Møller polarimeter. As a preliminary consistency check, the (linear) polarisation observable, Σ, was compared to world data for π^0 and η photoproduction. To determine the degree of circular polarisation, a Møller polarimeter was setup and first measurements of the electron beam polarisation performed.
